Unite PDFs:

	pdfunite $(ls *.pdf | sort -n) union.pdf


Rotate 90 degress clockwise:

	pdftk union.pdf cat 1-endeast output 1.pdf


Split vertically (use -x for horizontal split):

	mutool poster -y 2 1.pdf


Split into separate files, one page per file:

	pdfseparate out.pdf %d.pdf


Check Djvu metadata:

	djvused -e print-meta book.djvu


OCR:

	To see list of languages:
		tesseract --list-langs

	To perform OCR (overwrites existing OCR layer):
		ocrmypdf -l rus+eng+fra --redo-ocr --tesseract-timeout 3600 --tesseract-non-ocr-timeout 3600 -O 0 input.pdf output.pdf

